Date: Fri, 21 Jul 1995 14:24:43 -0400 (EDT)
From: Adam Thodey <athodey@engin.umich.edu>
Subject: Re: IMG tag and allowed image types...
To: lilley <lilley@afs.mcc.ac.uk>
Cc: www-html@www10.w3.org
In-Reply-To: <8330.9507211757@afs.mcc.ac.uk>
Message-Id: <Pine.3.87.9507211443.C755-0100000@chinook.engin.umich.edu>
How would I set up the IMG tag such that would allow many different
formats to be downloaded depending on the users WEB browser?
Would be be done, by lets say I had image type foo, bar, etc... and just
used:
<IMG SRC="imagename">
would that automatically look for types or how would that work?
Thanks again,
ADAM
On Fri, 21 Jul 1995, lilley wrote:
> Adam Thodey wrote:
>
> > I was wondering if there was a standard (i did not notice this in the
> > 3.00 spec) which would only allow certain types of graphics, i.e., GIF,
> > XBM etc.?
>
> No, ther eis not one in the standard, nor is there likely to be.
>
> > Would this mean that if the browser supports inline JPEGS or inline TIFF
> > or inline PICT that this is acceptable HTML inclusion?
>
> There are two questions here that need to be disentangled.
>
> 1) If my browser supports inline foo is it acceptable for my browser
> to request an inline image of type foo? The answer is yes. If the
> server has that image in format foo it will send that by preference.
>
> It is more likely that your browser will say it can accept inline images
> in several formats: foo bar etc and the server will send whichever of these
> it has (or an error saying, nothing suitable was found).
>
> This is called content negotiation and relies on the client expressing
> which formats it can accept and the server being able to supply the various
> formats; possibly by performing a conversion on the fly. Not all clients
> and not all servers can do this. Also, most content authors link to
> explicit formats. Also, image format conversion while maintaining quality
> is not as simple as it looks.
>
> 2) If my browser supports inline foo should I write pages with an
> explicit link to image.foo
>
> The answer is, it depends on your audience. If you are fairly sure they
> can all read foo format that is fine. For example because they all have
> a particular browser (a browser demo or fan club page for example).
>
> In general though, no assumptions can be made; in general, servers do not
> do image format conversion on the fly (if anyone has written a server or
> server extension that does, feel free to drop me a line as I would like
> to test it). So it is a case of authoring what the maximum number of people
> can already accept inline.
>
> GIF87a is a safe bet.
>
> GIF89a (the one with transparency) is extremely common and GIF87a
> readers can read it, they just ignore the extensions.
>
> XBM is pretty widespread
>
> JPEG JFIF is now common
>
> other formats supported inline include
>
> PICT (some Mac browsers, only)
> NCSA HDF (NCSA Mosaic for X, only)
> PNG (Amiga Mosaic so far)
>
> Chimera supports just about any format inline, as it is user extendable.
>
> > or is there going
> > to be a strict standard for image types?
>
> Clearly, this list will evolve over time. Once popular formats may become
> used less (so newer browsers stop supporting them); newer formats may become
> more popular. This is why the HTML standard does not dictate a list of
> acceptable inline image formats.
>
> --
> Chris Lilley, Technical Author
> +-------------------------------------------------------------------+
> | Manchester and North HPC Training & Education Centre |
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> | Computer Graphics Unit, Email: Chris.Lilley@mcc.ac.uk |
> | Manchester Computing Centre, Voice: +44 161 275 6045 |
> | Oxford Road, Manchester, UK. Fax: +44 161 275 6040 |
> | M13 9PL BioMOO: ChrisL |
> | URI: http://info.mcc.ac.uk/CGU/staff/lilley/lilley.html |
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>
>
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| Adam M. Thodey athodey@engin.umich.edu |
| Personal Homepage on the WEB http://www.engin.umich.edu/~athodey |
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